The human spine is a biomechanical structure consisting of thirty-three vertebral members and is responsible for protecting the spinal cord, nerve roots and internal organs of the thorax and abdomen. The spine also provides structural support for the body while permitting flexibility of motion. In certain surgical procedures it is necessary to secure together two or more of the vertebral members. The procedure may be necessary for example as a result of physical trauma or degenerative diseases.
One type of surgical procedure includes attachment of a vertebral plate to the vertebral members. The vertebral plate is sized to extend across two or more of the vertebral members. One or more bone screws extend through screw holes in the plate and into the vertebral members to secure the plate. One issue with the attachment is that the screws may tend to loosen and back-out of the vertebral members. Screw retention devices may be necessary to prevent the screw from backing-out of the vertebral members. While a variety of anti-backout approaches have been proposed, there remains a need for alternative designs.